Glass fibers destined for use as reinforcing elements in resinous materials ordinarily have a sizing composition, typically containing a polymeric or resinous film-forming component, a glass-resin coupling agent such as an organosilane, and such other components as lubricants, antistatic agents, etc., in dilute solution or dispersion in a volatile liquid solution, applied during their manufacture, preferably before they are gathered together in multi-filament strands. The amount of sizing composition so applied is adapted to result in the deposit of a very light-weight size coating on the glass fibers after any losses of liquid sizing composition from the fibers during processing and evaporation of volatile components from the liquid sizing composition remaining on the fibers, which may take place either before or after the fibers or multi-filament strands thereof are collected into a package as by winding into a rotating collet.
Sizing glass fibers is done for several purposes. Both before and after evaporation of volatile components, the sizing composition protects the glass fibers from being weakened as a result of abrasion during processing and handling. The sizing composition can also serve to help integrate the individual fibers of a multi-fiber strand into a more or less coherent unit. Finally, the dried size coating, while continuing to protect the fibers from mutual abrasion and to integrate multi-filament strands, can also facilitate the wetting of the coated fibers by a fluid material which will form a solid resinous matrix in which the fibers are imbedded as reinforcing elements and enhance the coupling between the cured resinous, matrix and the glass fibers so as to produce a more effectively reinforced composite material.
For applications in which higher tensile strength in the glass fiber reinforcing elements is desired, the fibers can advantageously be made from magnesium aluminosilicate glass compositions, such as described in U.S. Pat. No. 3,402,055 issued Sept. 17, 1968 to Harris and Machlan for Glass Composition and incorporated herein by reference. Heretofore, such fibers have been used primarily as reinforcing elements in epoxy resin matrixes but their use in such other resinous matrixes as polyesters, vinylesters, etc., is now becoming desirable.
The present invention provides improved sizings for such high-strength magnesium aluminosilicate glass fibers, and particularly sizings compatible with matrixes of such other resins as unsaturated polyesters, vinylesters, etc., as well as epoxides.